On October 28, 2003, 19-year-old Harvard University sophomore Mark Zuckerberg is dumped by his girlfriend, Erica Albright. Returning to his dorm, Zuckerberg writes an insulting post about Albright on his LiveJournal blog. He creates a campus website called Facemash by downloading photos of female students from house face books, then allowing site visitors to rate their attractiveness. After traffic to the site crashes parts of Harvard's computer network, Zuckerberg is given six months of academic probation. However, Facemash's popularity attracts the attention of twins Cameron and Tyler Winklevoss and their business partner Divya Narendra. The trio invites Zuckerberg to work on Harvard Connection, a social network exclusive to Harvard students and aimed at dating. Zuckerberg approaches his friend Eduardo Saverin with an idea for Thefacebook, a social networking website that would be exclusive to Ivy League students. Saverin provides $1,000 in seed funding, allowing Zuckerberg to build the website, which quickly becomes popular. When they learn of Thefacebook, the Winklevoss twins and Narendra are incensed, believing that Zuckerberg stole their idea while misleading them by stalling development on the Harvard Connection website. They raise their complaint with Harvard President Larry Summers, who is dismissive and sees no value in disciplinary action on Thefacebook or Zuckerberg.
Saverin and Zuckerberg meet fellow student Christy Lee, who asks them to "Facebook me," which impresses them. As Thefacebook grows in popularity, Zuckerberg expands the network to Yale, Columbia, and Stanford. Lee arranges for Saverin and Zuckerberg to meet Napster co-founder Sean Parker, who presents a "billion-dollar" vision for the company. Zuckerberg is impressed, but Saverin dismisses him as paranoid and delusional. Parker also suggests dropping "the" in Thefacebook and simply renaming the site to Facebook. Later, Zuckerberg relocates the company to Palo Alto on Parker's advice; Saverin remains in New York to work on business development. Parker later moves into the house that Zuckerberg is using as a base of operations and becomes more involved with the company, much to Saverin's annoyance.
While competing in the 2004 Henley Royal Regatta for Harvard against the Hollandia Roeiclub, the Winklevoss twins discover that Facebook has expanded to Europe with Oxford, Cambridge and LSE, and decide to sue the company for intellectual property theft. Meanwhile, Saverin objects to Parker making business decisions for Facebook and freezes the company's bank account in the resulting dispute. He relents when Zuckerberg reveals that they have secured $500,000 from angel investor Peter Thiel. After traveling to the company's new headquarters on the pretense of attending a business meeting and "millionth user party," Saverin becomes enraged when he discovers that the new investment deal allows his share of Facebook to be diluted from 34% to 0.03%, without diluting the ownership percentage of any other owner. He confronts Zuckerberg and Parker, and Saverin vows to sue Zuckerberg. Saverin's name had already been removed from the masthead as co-founder and CFO; Parker tells him that he is no longer a part of Facebook and has security eject him from the building. Later, Parker is apprehended for cocaine possession with a minor at a party celebrating one million users. He attempts to blame Saverin, so Zuckerberg cuts ties with him, telling him to go home.
In separate depositions, the Winklevoss twins claim that Zuckerberg stole their idea, while Saverin claims his shares of Facebook were unfairly diluted when the company was incorporated. Marylin Delpy, a junior lawyer for the defense, informs Zuckerberg that they will settle with Saverin since the sordid details of Facebook's founding and Zuckerberg's callous attitude will make him unsympathetic to a jury. Alone, Zuckerberg sends a Facebook friend request to Albright and repeatedly refreshes the page.
